In general, a constant voltage generation device is designed to includes a reference voltage generator, a differential amplifier and an output circuit. The reference voltage generator generates a reference voltage of a predetermined level. The output circuit generates an output voltage, which is controlled to be constant. The differential amplifier is supplied with the reference voltage and the output voltage to provide the difference between them. In response to the output signal of the differential amplifier, the output circuit is controlled to output a constant output voltage.
In such a constant voltage generation device, some noises may enter into the reference voltage and cause problems. Especially if short wave noises are successively entered into the reference voltage, the output voltage is oscillated.